Solid electrolyte separator, secondary battery, battery pack, and vehicle

A secondary battery comprising:

• a first electrode which is one of a positive electrode and a negative electrode;
• a second electrode which is the other of the positive electrode and the negative electrode;
• and
• a solid electrolyte layer which is a sheet comprising a solid electrolyte having a lithium ion conductivity,
• wherein a first lithium ion conductivity in a peripheral edge region along an in-plane direction of the sheet is lower than a second lithium ion conductivity in a central region along the in-plane direction of the sheet,
• wherein
• the solid electrolyte layer has a first surface and a second surface facing the first surface,
• at least a portion of the first surface is in contact with the first electrode, at least a portion of the second surface is in contact with the second electrode,
• a width of the first electrode along each direction of in-plane direction of the sheet is larger than a width of the second electrode along the each direction,
• the peripheral edge region is a region corresponding to a difference between the width of the first electrode and the width of the second electrode and comprises a first portion which comprises a surface in contact with the first electrode and located in the first surface,
• the central region is a region corresponding to the width of the second electrode along the each direction and comprises a second portion which comprises a surface in contact with the first electrode and located in the first surface, the second portion further comprises a surface being in contact with the second electrode and located in the second surface, and
• a first lithium ion conductivity of the first portion is lower than a second lithium ion conductivity of the second portion.